In UMTS wireless networks, devices are able to both initiate and perform simultaneous voice and data communication sessions. Such a simultaneous session is referred to as a multi-radio access bearer (multi-RAB or mRAB) call. Any time there is a multi-RAB call in progress, the mobile device necessarily shares hardware resources between the voice call and data sessions. Such resources include power, memory, processors, physical channels, transceivers, and the like. When there is a multi-RAB call, the circuit-switched voice channel utilized in the voice call tends to be less reliable and may have a higher dropped call rate.
One of the key differences between a circuit switched call and a mRAB call are the spreading factors used across the various radio access bearer configurations. The higher rate packet switched radio access bearer typically utilizes lower spreading factors, and therefore lower processing gains. However, this same spreading factor is used across the entire physical channel, which includes the logical channels (such as the circuit switched radio access bearer and the signaling radio bearer) that are mapped onto that physical channel. The lower spreading factor correlates to a lower processing gain for the signaling radio bearer.
Moreover, during mRAB calls, there is much more signaling between the UMTS Radio Access Network (UTRAN) and user equipment (UE) across the signaling radio bearer than there may be during a circuit switched call. Frequent radio bearer reconfigurations during mRAB calls may slow updates to the control link between the base station and the UE. If the packet switched bearer is dropped during such updates, there may be an interrupted data flow. If the signaling radio bearer breaks down even momentarily, there may be dropped voice call. The stress on the signaling radio bearer may be exasperated under heavy network loads or rapidly changing signal to noise ratios.
There has been massive growth in social networking and with the proliferation of smart phones, those social networking applications have naturally migrated into the wireless communication space. Many of those applications have features that permit near-real time updates of status, preferences, and other notifications. Such updates may occur as often as every few minutes, and in a smart phone environment, may force an ongoing circuit-switched voice call into a multi-RAB session without the user ever knowing that is the case. Thus even if the user were not to initiate a data session while on a voice call, the user may nonetheless be subject to the lesser reliability associated with a multi-RAB session.
Accordingly, there is a need for a solution that enhances the reliability of a voice call in an environment in which multi-RAB calls are not only possible, but may be initiated transparently to the user.